A Guide to the Kensai Magus (Pathfinder)
In both AD&D 2nd Edition and D&D 3rd Edition, the kensai was tied most heavily to the fighter class. For 2nd Edition, the kensai was a fighter “kit,” (which were much like Pathfinder’s archetypes), and in 3rd Edition, the kensai was a prestige class intended primarily for fighters (the kensai of the 3.5 revision was notably different from the original 3rd Edition one, representing something more along the lines of a samurai warrior than the “weapon master” concept of the previous two versions). Pathfinder bucks the trend and makes the kensai a magus archetype (Ultimate Combat 55), intended to represent a warrior with a mystical connection to a particular type of weapon.
At 1st level, the kensai gains proficiency with simple weapons and a single martial or exotic weapon. Unlike a normal magus, the kensai is not proficient in any armor and suffers normal arcane spell failure chances when wearing it. In exchange for his extra weapon proficiencies and armor proficiency, the kensai gains weapon focus with his chosen weapon and also gains the canny defense ability of the duelist, allowing to add his Intelligence modifier to Armor Class (up to one point per class level). This means he’s going to have lower AC than normal for a few levels, until his level catches up to his high Intelligence, but he does have his magic to back him up in that respect.
Additionally, kensai can cast one fewer spell of each level than normal, as part of the general trade-off for their enhanced martial prowess, hammering home the idea that they’re supposed to rely on their weaponry more so than other magi.
Upon gaining 4th level, the kensai trades in his spell recall ability for perfect strike (not to be confused with the Perfect Strike feat), which allows him to spend 1 point from his arcane pool to maximize his weapon’s damage roll for a single attack. If he scores a critical hit, he can instead spend two points to increase his weapon’s damage modifier for that critical hit by 1. If your weapon has large damage dice (such as the bastard sword’s 1d10), you’ll favor the first option, but if you have an expanded critical range (such as the scimitar’s 18-20), you’ll probably get more bang for your buck out of the second option.
The kensai gains fighter training earlier than the standard magus, at 7th level, and he also counts as a fighter of his level – 3, rather than one of half his level. This gives him earlier access to these fighter feats, and opens up some feats normal magi can’t attain, like Critical Mastery. This does replace knowledge pool, one of the magus’s most versatile abilities, so it doesn’t come without cost.
Also starting at 7th level, the kensai’s iaijutsu ability lets him add his Intelligence modifier to his initiative rolls and make attacks of opportunity while flat-footed, and he can draw his weapon as part of making an attack of opportunity. The text isn’t particularly clear here, but the intent seems to be that the kensai threatens the space around him with his weapon even when he doesn’t have it in hand. This ability takes the place of the magus’s medium armor training.
Beginning at 9th level, with the critical perfection ability, the kensai adds his Intelligence modifier on attack rolls made to confirm critical hits, and he treats his magus level as his base attack bonus for the purpose of qualifying for Critical Focus and the chain of feats connected to it. This requires that the kensai give up the magus arcana he would normally gain at this level.
At 11th level, the kensai gains superior reflexes (in place of improved spell recall), allowing him to make additional attacks of opportunity in each round equal to his Intelligence modifier. This ability stacks with Combat Reflexes, as well, allowing the dedicated kensai the ability to really crank out attacks of opportunity.
In place of heavy armor at 13th, the kensai gains iaijutsu focus. He can draw his weapon as a swift action during surprise rounds, and he adds his Intelligence modifier to damage on attacks made during surprise rounds or against flat-footed foes. While largely situational, given the kensai’s high initiative modifier, he should be able to make use of this regularly.
Starting at 19th level, the kensai becomes an iaijutsu master, always gaining a roll of 20 for his initiative and becoming immune to surprise. This of course means that the kensai can make the great use of his iaijutsu focus ability he gained back at 13th level, since he’s rarely going to be anything but first in a combat. This ability replaces the standard magus’s greater spell access.
Finally, at 20th level, the kensai trades the true magus ability for the weapon mastery ability of the fighter, selected for his chosen weapon.
Taken all together, these abilities make the kensai a capable warrior, with nearly unique access to feats like Critical Mastery and a useful number of spells to make him a versatile combatant. If you’re looking to play a magus that focuses more on the melee end of things, the kensai is definitely worth consideration.
Your selection of feats and arcana will probably have a lot to do with your chosen weapon as a kensai, so one sample build can’t encompass all the possibilities. As an example, though, this build takes a fairly standard approach, choosing the scimitar for the expanded critical range (to use with the critical multiplier part of perfect strike). Arcane Accuracy is one of your best choices for an early arcana, and there's no reason for a kensai to pass it up. Extra Arcane Pool is there to allow the magus to use perfect strike more often. At 5th level, your feat options open up somewhat, and this build takes Extra Arcana to pick up another magus arcana. Spell Shield is the choice here (for those sticky situations when your lack of armor gets the best of you), but there are a lot of options.
Human Magus (Kensai) 5
Ability Scores (15 Point Buy): Str 14, Dex 13, Con 12, Int 17, Wis 10, Cha 8
Feats and Arcana
1 Weapon Focus (scimitar), Extra Arcane Pool, Combat Casting
3 Dodge, Arcane Accuracy
5 Extend Spell, Extra Arcana (Spell Shield)
The kensai will end up trickiest to play at lower levels, when your Armor Class is a concern, but once you’re high enough level to gain your whole Intelligence as a dodge bonus, you’ll have far fewer worries. Of course, with spells like mirror image and shield, you have options available to help you survive those tricky times. With Extend Spell, you’ll be able to keep these buffs up for much of the time, as well. As you gain levels, consider fighter-only feats, since you have special access to them, and consider especially Critical Mastery, since you’re one of the few characters that can access it. It synergizes well with the critical strike magus arcana, as well.
That’s my general advice for the kensai archetype. There’s a lot of other things you can do with it, depending on your weapon of choice (such as going for a reach weapon to leverage the insane number of attacks of opportunity the kensai can make). As always, feel free to explore other options and experiment—just keep the kensai’s strengths in mind as you do!